Effects of light on trace elements and triiodothyronine levels in plasma of mirror carp (Cyprinus carpio)

The changes of copper, zinc, iron, magnesium, manganese, and triiodothyronine as a result of short- and long-term isothermal exposure to light were determined in the plasma of mirror carp (Cyprinus carpio). Two groups of fish were subject to a 3-mo treatment that consisted of (1) 8 h of light followed by 16 h of darkness and (2) 16 h of light followed by 8 h of darkness at 25 C. No significant changes were recorded between the two groups at the beginning of the study. After 3 mo, the triiodothyronine and elements levels as well as the growth rates of fish in the long-time exposure period were significantly higher than those in the short-time exposure (p < 0.05).